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    <script>
        function fn(a){
            this.a = a
        }
        var obj={}
        var getNum = fn.bind(obj);
        getNum(2);//2
        console.log(obj.a);


// 使用递归求到20的斐波那契数列之和
var a=1
var b=1
var c=0
var d=0
function fn(n) {
    c++
    d=a+b
    if(c==20){return d}
    b=d
    a=b
}
console.log(d);
    </script>
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